Which would be the best user error message? a) invalid parameterb) you must type a user name to continue. c) enter a user name to continue. d) gotcha! type in your user name. e) point the cursor on user name and type one, .

The best user error message would be C in my opinion

Explanation:

It does not directly engage with the user and instead simply states the course of action needed which allows users to know what needs to be done without being overly detailed in instructions in Option E or overly engaged or informal.